Atrial fibrillation is one of the most common cardiac arrhythmia. Health consequences associated with atrial fibrillation include decreased cardiac output, less regular ventricular rhythm, the formation of blood clots in the atrial appendages, and an increased incidence of stroke. While some drugs are available for the treatment of atrial fibrillation, they have a number of side effects which reduce their therapeutic utility.
Atrial fibrillation may be treated by the “maze procedure”. The maze procedure is a surgical technique that involves the formation of a pattern of incisions in the left and/or right atrial walls. This procedure is intensely invasive with a difficult recovery, and it has accordingly been desirable to establish less invasive, closed-heart, catheter based techniques for treating atrial fibrillation.
Swartz et al., U.S. Pat. No. 5,690,611, describes a process for the treatment of atrial arrhythmia in which a catheter is introduced into the left or right atrium through a guiding introducer and a pattern of ablation tracks formed therein. A problem with this technique is that an extensive number of lengthy ablation tracks are formed, and since linear lines are formed by slowly dragging the catheter procedure time is extensive.
Avitall, U.S. Pat. No. 5,687,723, describes a mapping and ablation catheter for treating atrial fibrillation. The device is designed to produce linear lesions from an array of mapping and ablation electrodes serially positioned along the catheter. A vascular guide wire is included fixed to the distal tip of the catheter to help navigate the device. The hook-shaped vascular guide wire may be inserted into a pulmonary vein and anchored therein, apparently by a hooking action, to help adjust the electrode-carrying segment of the catheter (FIGS. 14-15; column 9). However, Avitall still necessitates elongate linear lesions in the manner described by Swartz et al.
H. Calkins et al., Am. J. Cardiol. 83, 227-23 6D (1999), describes a system that incorporates multiple preshaped steerable catheters. The pre-shaped steerable catheters are formed by embedding a preshaped Nitinol stylet in the shaft thereof. The catheters can deliver a variety of lesion shapes, from localized spot lesions to lesions that are 8 centimeters in length.
Recent studies have suggested that focal arrhythmia can originate from a tissue region along the pulmonary veins extending from the left atrium, particularly the superior pulmonary veins. For example, Lesh et al., U.S. Pat. No. 6,012,457, provide a device that forms a circumferential lesion and circumferential conduction block in a pulmonary vein. The device is a balloon that carries a circumferential electrode, and extends over a guidewire through the atrium and into, or partially into, a vein. The balloon centers and secures the device in the vein, where the electrode ablates a circumferential region of tissue within the vein, or within the vein and extending out into the atrium. While this device reduces the amount of tissue that must be ablated to a smaller circumferential pattern, a problem with this approach is that the ablation of tissue within the vein can lead to pulmonary vein stenosis, which may induce pulmonary hypertension. See, e.g., I. Robbins et al., Circulation 98, 1769 (1988); G. Taylor et al., Pace 22 (Part II), 712 (1999).
Accordingly, an object of this invention is to provide a closed-heart procedure for treating atrial arrhythmia in which the region of tissue ablation is reduced, yet the ablation of tissue within a pulmonary vein is avoided.